The present invention is related generally to pressure transducers and particularly to the isolation of the pressure sensing elements of the pressure transducer from the media that represents the pressure to be measured.
A barrier diaphragm is commonly used to separate pressure sensing elements from the media whose pressure is being measured. This is done in order to protect the pressure sensing element from electrically conductive or chemically active media. Frequently, the sensing element operates in some form of oil or hydraulic fluid which serves to transmit pressure from the back side of the barrier diaphragm to the sensing element. In this manner, the harsh media remains on the outside of the barrier diaphragm while the sensing element is protected in a benign fluid. Barrier diaphragms are typically made from stainless steel or similar material and are typically 0.002 includes to 0.004 inches thick, resulting in a delicate member which must be protected from physical contact with anything that might dent or deform the diaphragm. Pressure measurement errors of a temporary or permanent nature will result if the diaphragm is deformed from the shape that existed when the transducer was calibrated.
Certain applications of pressure transducers require the transducer to operate in an environment where the liquid media, whose pressure is being measured, is mixed with solid particles which have the capability to dent and deform a barrier diaphragm, thus producing temporary or permanent measurement errors. One example of this is when liquid media is trapped in the porous rock formations beneath the surface of the earth. In this example, the pressure transducer is forcibly inserted into the porous rock and the liquid media is allowed to enter the transducer where the pressure is measured. Rock fragments coming in contact with a barrier diaphragm would cause measurement errors. Another condition having the capability to damage barrier diaphragms are high acceleration forces present when a pressure transducer is forcibly inserted into porous rock. Under high g-forces, the mass of the diaphragm and the hydraulic fluid behind it can permanently deform the diaphragm, thus producing permanent calibration errors in the transducer.
Another example of a media that could damage a barrier diaphragm would be where a pressure transducer is used to measure the pressure of a mixture of a liquid and particles in a pipeline, such as a pipeline used for transporting a slurry.
Thus a need exists for a pressure transducer that isolates the media being measured from particles contained in the media and is tolerant of the high acceleration forces that the transducer may be subjected to in certain applications.